Accumulator with refrigerant level indicating means

ABSTRACT

A dead-end tube extending from the side wall of the accumulator in a flooded evaporator refrigeration system having a fixed expansion device, for indicating the level of liquid refrigerant in the accumulator to facilitate the charging of the system. The tube is located at a position coincident with the liquid refrigerant level in the accumulator existing when the system has an optimum charge of refrigerant at predetermined operating conditions. To charge the system, it is run at the predetermined operating conditions while adding refrigerant, until the tube sweats or frosts over to indicate that the liquid level has reached the tube.

United States Patent 1191 Kuttruff et al.

[ ACCUMULATOR WITH REFRIGERANT LEVEL INDICATING MEANS [75] Inventors: Gary W. Kuttrufi, North Syracuse;

Raymond F. Durham, Liverpool,

[ Sept. 24, 1974 Primary ExaminerMeyer Perlin Attorney, Agent, or FirmJ. Raymond Curtin; D. Peter Hochberg [5 7] ABSTRACT A dead-end tube extending from the side wall of the accumulator in a flooded evaporator refrigeration system having a fixed expansion device, for indicating the level of liquid refrigerant in the accumulator to facilitate the charging of the system. The tube is located at a position coincident with the liquid refrigerant level in the accumulator existing when the system has an optimum charge of refrigerant at predetermined operating conditions. To charge the system, it is run at the predetermined operating conditions while adding refrigerant, until the tube sweats or frosts over to indicate that the liquid level has reached the tube.

1 Claim, 1 Drawing Figure ACCUMULATOR WITH REFRIGERANT LEVEL INDICATING MEANS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the charging of flooded evaporator refrigeration systems having fixed metering devices, and in particular to the charging of an accumulator in such a system according to the level of liquid refrigerant in the accumulator.

2. Description of the Prior Art A common type of flooded evaporator compression refrigeration system incorporates an accumulator disposed between the evaporator and the compressor. A main function of the accumulator is to assure a proper supply of refrigerant in the system under all operating conditions, i.e. regardless of the compressor flow rate. When the compressor flow rate is at its minimum value, the accumulator capacity must be sufficient to store excess refrigerant without allowing any liquid to flood into the compressor. On the other hand, when compressor flow is at a maximum value, the accumulator must have enough liquid refrigerant to assure a flow of sufficient refrigerant to prevent freeze-up of the evaporator coil. The accumulator also serves to separate out the liquid portion of refrigerant fed thereto to prevent the passage of liquid refrigerant into the compressor. An accumulator generally comprises a housing having an inlet line from the evaporator for receiving refrigerant from the evaporator, and a discharge line above the liquid level in the accumulator for discharging refrigerant vapor into the suction line of the compressor.

It is well known in the art that any refrigeration system functions most efficiently when it has an optimum charge of refrigerant in the system, this optimum charge being dependent upon various parameters of the system. Accordingly, the optimum refrigerant charge for a flooded evaporator compression refrigeration system having an accumulator and a fixed expansion device can be expressed in terms of the level of liquid refrigerant in the accumulator when the system is operating at given conditions. If theoptimum charge were so expressed and the level of refrigerant in the accumulator were easily determinable, charging the system would be a relatively routine operation. It is known to employ a sight glass on the accumulator to observe the liquid level therein, but variations in the ambient return air often change the compressor flow rate, whereby the desired liquid level in the accumulator varies as well. If the evaporator fan is shut off to avoid the effect of the ambient return air, frost forms over the entire accumulator, so that the use of such sight glasses is prohibited. Therefore, a common prior method of charging such a refrigeration system requires the incorporation of a sight glass on the discharge line from the condenser ahead of the expansion device leading to the evaporator. Refrigerant is added to the system until the sight glass clears (i.e. until no gaseous refrigerant is visible in the glass), and a predetermined amount of additional refrigerant is added to the system. In addition to the inconvenience and expense of requiring a scale to weigh the additional refrigerant, the foregoing method has inherent shortcomings. For Example, if the sight glass is initially clear, the amount of additional refrigerant required cannot accurately be determined, so that over-charging or under-charging is very possible. In order to overcome this possibility, it is usually necessary to remove refrigerant from the system until the sight glass displays refrigerant bubbles and then to add refrigerant as described above.

US. Pat. No. 3,162,021, which issued to H. M. Brody on Dec. 22, 1964, provides a refrigeration system including apparatus for charging the system. That system is quite complex and expensive because it requires the addition of a receptacle on the discharge side of the evaporator, and a series of tubes extending from the side wall of the receptacle which terminate in restrictors leading to the suction line of the compressor. The system is charged by closing off the evaporator and circulating refrigerant through the receptacle and the restrictors to the compressor, and by adding refrigerant to the system until condensate or frost accumulates on a desired one of the tubes extending from the rectptacle. As will be apparent from the description below, the present invention also relies on the accumulation of frost or condensate on a tube extending from a receptacle for indicating the level of liquid refrigerant in the receptacle, but the present invention requires virtually no additional parts (since the receptacle is already in the system) and can be used to charge the system during the substantially normal operation thereof, without necessitating the redirection of refrigerant flow in the system.

SUMMARY OF THE INVENTION An object of the present invention is to charge a flooded evaporator compression refrigeration system having an accumulator and a fixed expansion device, in an economical, simple, and accurate manner.

A further object of the invention is to provide means and a method for charging such a system in a simple manner requiring minimal equipment. Other objects will be apparent from the description to follow and from the appended claims.

According to a preferred embodiment of the invention, there is provided a dead-end tube extending from the side wall of an accumulator in a flooded evaporator compression.refrigeration system having a fixed expansion device. The dead-end tube is located at the liquid refrigerant level which exists in the accumulator when the sytem is charged with an optimum amount of refrigerant under given operating conditions. The tube extends sufficiently from the accumulator tank into the ambient surroundings so that neither frost nor substantial condensate will collect thereon when the level of liquid refrigerant in the accumulator is below the level at which the tube is disposed, whereby the dead-end tube either frosts or sweats only when liquid refrigerant enters the tube. Thus, a visual observation of the tube as the system is charged under the foregoing given operating conditions, indicates when the liquid refrigerant level has reached the tue and when the optimum charge has been achieved.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing shows a side cut away view of an accumulator according to the present invention, as incorporated in a schematically shown compression refrigeration system.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the preferred embodiment, there is provided a substantially conventional accumulator located on the suction side of the compressor in a compression refrigeration system. The accumulator has an inlet near its upper portion for receiving refrigerant from the evaporator. An outlet conduit extends from an upper portion of the accumulator to the suction line of the compressor for directing vaporized refrigerant from above the liquid refrigerant level in the accumulator to the compressor. A closed or dead-end tube extnds from a side wall of the accumulator at a position which coincides with the liquid refrigerant level which exists in the accumulator when the refrigeration system has an optimum refrigerant charge under predetermined operating conditions. When the system is operating under such conditions, refrigerant can be charged into the system so as to raise the liquid level in the accumulator until the liquid refrigerant enters the dead-end tube, at which time the tube frosts over or sweats. This indicates that the liquid refrigerant level has reached the desired height and that the charging operation should cease.

Referring now to the drawing, a compression refrigeration system is depicted which comprises a compressor l, a condenser 3, a capillary tube or other fixed expansion device 5, a flooded evaporator 7 and an accumulator 9. The foregoing components are connected by refrigerant conduits to form a refrigerant flow circuit. Thus, hot gaseous refrigerant is compressed in compressor 1 and directed to condenser 3, where it transmits heat to a heat exchange medium passing over the condenser, causing the refrigerant to condense. Liquid refrigerant is discharged from the condenser to expansion device which reduces the pressure of the refrigerant and feeds it to evaporator 7. A fan 10 driven by a motor 11 blows air over the evaporator to transmit heat to the refrigerant therein, causing a portion of the latter to vaporize. Hot liquid and saturated vapor proceed from evaporator 7 to accumulator 9. Any liquid discharged from evaporator 7 is accumulated in accumulator 9, and vaporized refrigerant is fed to the suction line of compressor 1 to complete the cycle.

Accumulator 9 acts as a surge tank for flooded evaporator 7, taking any excess refrigerant liquid from the evaporator. The accumulator also separates out the liquid portion of the discharge of evaporator 7 so that only vaporized refrigerant is fed to compressor 1.

Accumulator 9 comprises a vertically standing cylindrical shell 12 having a base 13 and a cap 15 which are attached to shell 12 in a fluid tight fashion to define a chamber for receiving refrigerant. Refrigerant from evaporator 7 enters accumulator 9 through an inlet pipe 17 which extends through shell 12 near the upper portion of the accumulator. The means of discharging vaporized refrigerant from the accumulator comprises a standpipe 19 which is mounted vertically in acumulator 9 and extends from an entrance portion 21 located near the top of accumulator 9 to an outlet 23 which extends through base 13 of the accumulator. The seam between outlet 23 and base 13 is soldered or otherwise sealed in a fluid tight manner. The level of liquid refrigerant in accumulator 9 is always kept below inlet pipe 17 and entrance 21 of standpipe 19 so that only vaporized refrigerant can exit from the accumulator.

A dead-end tube 25 extends radially outwardly from shell 12 at a location which has been predetermined to coincide with the level of liquid refrigerant in accumulator 9 occurring when the system has an optimum charge of refrigerant under given operating conditions.

Tube 25 is opened at one end to the interior of accumulator 9 and closed at its other end, so that liquid refrigerant enters the tube when the level of liquid refrigerant in the accumulator reaches the level at which the tube is located. Tube 25 is of a sufficient length so that neither frost nor condensate accumulate on the exterior portion thereof unless liquid refrigerant has actually entered the tube. In other words, the tube must be of sufficient length so that ambient air maintains at least a substantial portion of the tube above the dewpoint temperature until the entry of liquid refrigerant into the tube.

A fusible plug 27 is attached to a coupling 29 extending from cap 15 of the accumulator. Plug 27 normally forms a fluid tight seal with coupling 29, but is releasable in response to an increase of temperature, whereby plug 27 functions as a safety device to limit the pressure build-up within the accumulator.

In order to charge the sytem shown in the drawing with refrigerant, evaporator fan motor 11 is turned off to eliminate any variation in the conditions of refrigerant entering accumulator 9, and the head pressure is maintained within a prescribed range such as by blocking the coil of condenser 3. The system is then run for several minutes while observing the exterior surface of tube 25. If ,tube 25 does not frost over within this period, there 'is'an insufficient refrigerant charge in the system. In the latter'case, refrigerant is added to the system through an appropriate valve 31 located in the suction line of compressor 1, until tube 25 frosts over or sweats by virtue of the level of liquid refrigerant in accumulator 9 having reached the tube. lf tube 25 frosts over during the foregoing period, refrigerant can be bled from the system until the tube clears, and refrigerant is then introduced through valve 31 until the tube frosts or sweats.

The foregoing arrangement works very well for accumlators designed for use in particular systems wherein there is only one optimum liquid refrigerant level in the accumulator under the given cnditions. It is possible to incorporate a plurality of charging tubes at various heights on the accumulator to indicate a plurality of liquid refrigerant levels in the accumulator. The latter arrangement would enable the production of a single accumulator for use in refrigeration systems having different optimum charges.

It can be seen that the present invention achieves all of the objects set forth above. The invention is extremely simple in use and obviates the need for scales or other weight measuring equipment which are conventionally used in the charging of refrigeration systems. Moreover, the foregoing charging method and apparatus avoid the loss of refrigerant during the charging process and they minimize the effect of outdoor and indoor air conditions. a

The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A refrigerant accumulator for use in a flooded evaporator compression refrigeration system having a fixed expansion device, said accumulator comprising:

wall means defining a chamber for receiving refrigerant;

level in said chamber when the system has an optimum charge of refrigerant under predetermined operating conditions, said tube receiving liquid refrigerant when said level is attained and the exterior surface of said tube collecting frost or condensed moisture in response to the entry of liquid refrigerant into said tube. 

1. A refrigerant accumulator for use in a flooded evaporator compression refrigeration system having a fixed expansion device, said accumulator comprising: wall means defining a chamber for receiving refrigerant; an inlet to said chamber; an outlet for directing vaporized refrigerant from said chamber; a tube extending horizontally outwardly from said wall means and terminating in a free end, said tube being closed at said free end and having a single opening at the juncture of said tube with said wall means into said chamber at the liquid refrigerant level in said chamber when the system has an optimum charge of refrigerant under predetermined operating conditions, said tube receiving liquid refrigerant when said level is attained and the exterior surface of said tube collecting frost or condensed moisture in response to the entry of liquid refrigerant into said tube. 